This application claims priority from Japanese Patent Application No. 2002-000169 filed Jan. 4, 2002, which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a liquid reserving or storing device or reservoir that can reserve or store a liquid.
2. Description of the Related Art
For ink-jet printing apparatuses, a large number of means have been proposed and put to practical use which supply ink to an ink-jet print head from which the ink can be ejected.
The capillary force of nozzles in the ink-jet print head is utilized to supply ink to the ink-jet print head. Accordingly, the external force of pressurizing means, such as a pump, is not required. Thus, except for special cases, it is unnecessary to have a mechanism that delivers ink under pressure from an ink supply tank to the ink-jet print head. On the other hand, to continuously eject ink droplets stably through the nozzles in the ink-jet print head, the ink must be subjected to a very weak negative pressure of 100 to 2,000 Pa. This has been important in designing an ink-jet printing apparatus.
A classical ink supply method is known which is used for, for example, an ink-jet printing apparatus of a serial scan type such as the one shown in FIG. 1.
The printing apparatus in this example sequentially prints an image on a sheet 17 as a printing medium by alternately performing a printing operation of ejecting ink from an ink-jet print head 12 on the basis of image data while moving a carriage 11 with the mounted the ink-jet print head 12 in a main scanning direction shown by arrow A, and a transporting operation of transporting the sheet 17 in a sub-scanning direction shown by arrow B and crossing the main scanning direction. Reference numeral 15 denotes a guide shaft that guides the carriage 11 so as to be movable in the main scanning direction. Reference numeral 16 denotes a platen roller. Reference 18 denotes a cap that can cap a nozzle portion (ink ejection port portion) of the print head 12. The print head 12 can execute a recovery process for allowing ink to be ejected properly, by (preliminarily) ejecting ink that does not contribute to image printing, into the cap 18. Further, a suction recovery process can be executed to allow ink to be ejected properly, by introducing negative pressure into the cap 18 capping the print head 12 to suction ink out from an ink ejection port.
A configuration of the print head 12 can be employed which includes an electrothermal converter used to eject ink droplets through the ink ejection port. That is, the electrothermal converter generates heat to cause film boiling, so that the resulting bubbling energy is utilized to eject ink droplets through the ink ejection port.
A method of supplying ink in such a printing apparatus comprises supplying ink from an ink reserving or storing device 13 such as an ink bag through a tube 14 to the print head 12 mounted on the carriage 11 as shown in FIG. 1. With this method, to exert negative pressure on ink supplied to the print head 12, the ink reserving device 13 is arranged on a surface located several centimeters lower than the gravitational height (also referred to as a xe2x80x9cheadxe2x80x9d) of the print head 12. Thus, the method of exerting negative pressure using the head difference can be achieved inexpensively using a very simple structure. However, the installation site of the printing apparatus is limited to a flat place such as a desk, or the printing apparatus must be high in order to ensure the head difference. To solve these problems, many attempts have been made to provide the ink reserving device 13 with negative pressure generating mechanism.
FIGS. 2 and 3 illustrate a different conventional example of a negative pressure generating mechanism provided in the ink reserving device.
The negative pressure generating mechanism in FIG. 2 is provided with a metal spring 22 or the like in a flexible bag 21 in which ink is housed. The spring expands the bag 21 in the vertical directions of FIG. 2, shown by the arrows, to generate negative pressure in the ink 23 in the bag 21. Reference numeral 24 denotes an outlet from which the ink 23 is supplied from the bag 21 to the print head. On the other hand, the negative pressure mechanism in FIG. 3 is provided in a pressure regulating valve 31 in a case 30 that houses the bag 21 to control the air pressure in an outer area 32 around the bag 21. Thus, negative pressure is exerted on the ink 22 in the bag 21. That is, the pressure regulating valve 31 performs opening and closing operations so as to maintain a predetermined negative pressure in the outer area 32. When the pressure regulating valve 31 is opened, external air flows into the case 30.
However, a large number of parts are required by the negative pressure generating mechanisms that generate negative pressure in the flexible bag 21 as shown in FIGS. 2 and 3. This increases costs. Further, it is technically difficult to generate a negative pressure of the order of several hundred Pa. Furthermore, the presence of such a negative pressure generating mechanism may degrade the capability of storing available ink. Moreover, the thin bag 21 does not hinder passing of gas sufficiently, so that the open air may enter the bag 21 to expand it or evaporate the ink. Thus, many problems must be solved before the negative pressure generating mechanism can be added to the ink reserving method that uses the bag, while maintaining its reliability.
FIG. 4 is a sectional view of an ink reserving device that uses a sponge method, a presently popular ink reserving method. A sponge-like porous member (ink absorber) 41 can reserve ink on the basis of its own capillary force and can exert an appropriate negative pressure on ink when having a properly selected density. Reference numerals 40, 42, and 43 denote a case, an air intake port, and an ink outlet, respectively. Such a reserving method involves a very simple structure and allows the ink absorber 41 to be manufactured inexpensively by using a commercially available sponge-like porous member. Further, the size of the ink reserving device can be reduced, and the predetermined negative pressure can be generated regardless of changes in its position during operation.
However, general methods of manufacturing a sponge-like porous member do not provide a sufficiently dense porous member. Accordingly, the porous member must be compressed to some degree before use. This causes ink to be used inefficiently, so that the ink reserving device can generally be filled with ink only up to 70% of the volume of the sponge-like porous member. Further, it is difficult to arrange the sponge-like porous member uniformly in the ink reserving device. The nonuniform arrangement of the porous member may cause the ink to be used inefficiently. Further, a part of the ink-jet printing apparatus which contacts with ink is commonly composed of metal such as stainless steel or resin such as polypropylene, polyethylene, or a fluorine resin. When this metal or resin contacts with the ink, a very small amount of decomposed material or additive may dissolve. Many commercially available porous members are composed of a urethane resin and are thus relatively chemically unstable. In recent years, more chemically stable sponge-like porous members made of polypropylene have been employed. However, the sponge-like porous member contacts with ink over a large area and may thus chemically react to the ink or may be eluted into it. As a result, a large amount of product may affect the nozzles in the print head. On the other hand, various types of ink are used in order to enhance the applicability of the ink-jet printing apparatus. However, since the chemical stability of the sponge-like porous member is critical, it has been unavoidable to take proper measures such as changing the formation of the ink to improve its chemical stability, while sacrificing its physical properties.
FIG. 5 is a sectional view illustrating, as an example of another configuration of an ink reserving device, a configuration having functions equivalent to those of the sponge-like porous member, i.e., a configuration having functions of reserving ink and generating negative pressure. As described in Japanese Patent Application Laid-open Nos. 4-179553 (1992) and 3-139562 (1991), this ink reserving device attempts to reserve ink by stacking thin plates 51 together instead of using the sponge-like porous member. Ink reserving portions 53 are formed in the narrow gaps between the plates 51. Reference numerals 50 and 52 denote a case and an ink outlet, respectively. Reference numeral 54 denotes a buffer used to accommodate variations in pressure. Reference numeral 55 denotes a capillary member through which ink from the ink reserving portions 53 is guided to the ink outlet 52. Capillary force is used to reserve ink in the ink reserving portions 53 and generate negative pressure in them. The capillary force is expressed by the classical equation h=2Txc2x7Cos xcex8/(xcfx81xc2x7gxc2x7r). Where, h denotes a difference in liquid level between the interior and exterior of a tube, T is the surface tension of a liquid, xcex8 is a contact angle, xcfx81 is the density of the liquid, g is gravitational acceleration, and r is the radius of the tube. The ink reserving method using the thus stacked thin plates 51 involves a relatively simple structure. Consequently, it enables reliable dimension management compared to manufacture management used for the sponge-like porous member.
However, the ink reserving device in FIG. 5 requires the capillary member 55 to reliably obtain ink from the ink reserving portions 53. Desirably, the capillary member 55 must be arranged so as to penetrate the plates 51. The capillary member 55 must have capillary force stronger than that of the ink reserving portions 53 and thus has an excessive ink channel resistance. As a result, with a multi-nozzle ink-jet print head that uses a high drive frequency and thus consumes a large amount of ink, dynamic resistance associated with ink supply is increased to cause the ink to be exhausted prematurely.
All conventional ink reserving devices have problems to be solved, and it is desirable to provide an ink reserving device that can be manufactured inexpensively and still provide excellent functions.
It is an object of the present invention to provide a liquid reserving device which can be manufactured inexpensively, which allows various liquids such as ink to be used in a chemically stable manner, and which can stably supply a liquid by reducing channel resistance irrespective of changes in position during operation to generate a predetermined negative pressure.
There is provided a liquid reserving device that allows a liquid reserved in a liquid reservation chamber to be guided out from an outlet, wherein
a plurality of thin plates are disposed in the liquid reservation chamber at predetermined intervals to form a reserving portion in which predetermined capillary force is generated, and a predetermined gap is formed between the reserving portion and the outlet to form a guiding portion in which capillary force is generated which is stronger than the capillary force of the reserving portion.
According to the present invention, the reserving portions that generate predetermined capillary force are formed of the plurality of thin plates disposed at predetermined intervals. The predetermined gap provided between the reserving portion and the liquid outlet forms the guiding portion that generates capillary force stronger than that of the reserving portions. Thus, the simple configuration can be used to smoothly guide the liquid from the reserving portions through the guiding portion to the outlet. This provides an ink reserving device which allows various liquids such as ink to be used chemically stably and which can stably supply a liquid by reducing channel resistance irrespective of changes in position during operation to generate a predetermined negative pressure.
Further, by housing ink in the reserving portions and supplying it to the printing apparatus, the ink can be supplied stably to allow high-grade images to be printed stably.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.